A thank you doesn't pay the consequences of one's actions
Miguel I dropped 20 dollars man and I haven't ate in two days I'm starving! Here's a damn burger a thank you doesn't pay the fiddler!
A backronym for βtipβ or gratuity. Tipping can be seen as a way of thanking a person for good services, so βthanks in payβ works pretty well.
The waiter was friendly and attentive, so I thanked him with a good tip.
Ah, so a tip is a thanks in pay!